1. Field of the Invention
The present invention relates to a film rewinding system of a camera.
2. Description of the Related Art
Recent cameras are trending toward a camera having a motor driving mechanism through which a film feeding system carrying out film winding/rewinding and a cocking system cocking predetermined mechanisms are driven by an integrated motor in a camera body. Moreover, the abovementioned camera is a type of camera which have two motors and two driving mechanisms, whereby each of the film feeding system and the cocking system is driven independently. The reason why the camera is so arranged is based on the following advantages. That is, it is possible to transfer a release operation before completion of the film winding if the cocking is completed before initiation of the film winding. In addition, it is possible to increase a feeding speed of a frame of film roll. Further, the cocking is only requested at a multi-exposure or in the case of no film available. In addition to the above, normally, load characteristics of a film winding/rewinding process of the film feeding system and a cocking process of the cocking system are different from each other. That is, drive for the film feeding system has characteristic of increase of the load in the case where a temperature is low. On the other hand, the cocking system has characteristic of that the load characteristic is almost constant since the cocking system is comprises mechanical elements. Further, influence of a voltage-drop of a power source integrated in the camera body and the like has something to do with a driving characteristic of the motor. Under these circumstances, it is preferable that each of the cocking system and the film feeding system are driven individually and independently. Therefore, an exclusive motor and an exclusive driving mechanism for each system are provided in the camera body. And the cameras having such a structure (referred to as "two motors drive type") are provided widely. However, this type of cameras requires two motors and the respective driving mechanisms driving by the respective motors, so that a space accommodating them in the camera body causes a size of the camera body to be large. In addition, there is a further disadvantage that a time necessary for carrying out the film winding/rewinding is under certain restrictions in connection with the respective load characteristics described above even though the camera has the exclusive motor.
Further, in the above-mentioned camera, it is so arranged that the film rewinding process is automatically initiated when the film roll gets tense at its final frame in operation of the film winding. However, it is uncertain that shifting from the film winding to the film rewinding is always effected smoothly and immediately at film tension. That is, in the film winding process, feed of the film roll is controlled so as for a frame of the film roll to be fed one by one. In other words, the film feeding system is controlled so as to be restrained every frame. But, it is uncertain that the final frame of the film roll is always positioned at a proper location in the camera at completion of a photographing operation. There is possibility that the film tension may be caused on the way to the final frame. In this case, film winding means of the film feeding system does not come into its locked state. It means that the operation of the film feeding system is restrained by predetermined means (so-called lock means for locking the film winding means so that the film feeding system does not operate). On one hand, it is so designed, in the film rewinding process, that a lock operation of the lock means is restrained by a predetermined means so that the film roll is rewound continuously. Accordingly, if the lock means is located at its predetermined position, the rewinding operation is temporarily interrupted at the beginning of the rewinding process, resulting in that a smooth operation to the film rewinding process may be not expected.
It is to be noted, here, that if an additional means by which the lock operation of the lock means is restrained continuously in the rewinding process until the film rewinding operation is completed is provided, there is not caused the above-mentioned trouble if the film roll gets tense and does not travel from an intermediate position of the frame any more. However, the additional means is requested in the camera and the above countermeasure is not advantageous to the solution of the above-mentioned trouble.
On one hand, depending on a situation, there may happen to initiate the film rewinding operation from a halfway frame of the film roll. Accordingly, it is desirable that such a function is available even in the camera having the motor driven film winding system. But, as previously described, in the case of initiating the film rewinding operation from the halfway frame of the film roll, the film feeding system is the locked state so that the film rewinding operation may not be initiated immediately from such a state. That is, in the case where the film rewinding operation is initiated from the halfway frame of the film roll, it is necesssary to dis-lock the locked state at first. In one of the conventional type of cameras, a dis-locking operation of the locked state of the film feeding system depends on a photographer's operation in order to initiate the film rewinding operation from the halfway frame. That is, the photographer operates operation means, e.g., an operation button, for the film rewinding, which is associated with a dis-lock mechanism and orders the dis-lock mechanism so that the mechanism operates to dis-lock the locked state of the film feeding system. On the other hand, in the other of that, the following procedure is taken. That is, the film rewinding is so arranged that a halfway operation of a one-frame winding of the film roll is performed, at first, then a full operation of the film rewinding is initiated. In the former, not only a location of the operation means is restricted in the camera, but also the photographer has to operate the operation means at the completion of the film winding operation. Further, on operating the operation means, his finger is loaded so much. In the latter, an additional action, which is waste, of winding the film roll a little bit is requested, resulting in that the instant film rewinding at the completion of the film winding is not achieved.
Meanwhile, it is normally preferable with respect to the film rewinding of the camera that the rewinding is so arranged as for the film roll to be completely accommodated inside the patrone. The reasons depend on the following. One is to avoid a mistake that a photographed roll film is loaded in the camera since it can not distinguish from its appearance whether or not the roll film is a new roll film if the photographed roll film is not completely accommodated inside the patrone. Another is to avoid that a curtain of a shutter is wounded by an end portion of the film, which protrudes from the patrone, when the patrone is picked up out of the camera. Most of the cameras having the motor driven film winding system are such arranged due to these reasons.
In this type of cameras, a detection switch is provided, by which the completion of the film rewinding operation is detected. The camera is designed in such a manner that the detection switch operates at a state that the end portion of the film protrudes from the patrone a little bit and the motor is driven for a certain time under such a state and then the film roll is completely accommodated inside the patrone. The certain time is set to a time necessary for the film roll to accommodated in the patrone securely under the consideration of factors having influence upon the film rewinding, such as the voltage-drop, the change of the load characteristic of the film depending on the change of the temperature, and the like. If the time for driving the motor is set in such a way, there is caused no trouble. On the other hand, if the film rewinding is carried out under good conditions, the motor is driven continuously until the setting time is up nevertheless the film roll has been already accommodated in the patrone. It means that such an operation causes the following problems; waste consumption of the electricity and a longer operation time for the film rewinding.
Now, regarding the the above-mentioned, its concrete description proceeds, hereinafter.
The time to be taken from detecting the completion of the film rewinding until accommodating the film roll inside the patrone completely is determined depending on a driving characteristic of driver means by which the film rewinding means is driven. That is, if the driving characteristic of the driver means is characteristic of a high speed characteristic, a time as the setting time is short enough. On the other hand, if it is characteristic of a low speed characteristic, a long period as the setting time is necessary. Accordingly, if a time to be taken from detecting the completion of the film rewinding until turning the motor off is set to a time to be taken therebetween under the high speed characteristic driving, it wonders that a part of the film roll is not accommodated in the patrone under the low speed characteristic driving. On the contrary to the above, if the time is set to a time to be taken therebetween under the low speed characteristic driving, the driver means drives longer than necessary, resulting in that it causes waste consumption of the electricity and causes a disadvantage that a time necessary for rewinding becomes long.